Access Network For Digital Telecommunications System And Method Of Digital Telecommunications

ABSTRACT

An access network for terminals of a digital telecommunications system includes base stations adapted for receiving radiofrequency signals emitted by the terminals, each terminal a physical layer processing module adapted to form a radiofrequency signal on the basis of binary data in accordance with a predefined physical layer protocol. Moreover, for at least one base station, termed the “partial station”, an inverse physical layer processing, making it possible to extract binary data from a radiofrequency signal, is distributed between the partial station and a processing server distinct from the partial station, an inverse physical layer processing module being made up of a first inverse processing module, integrated into the partial station, and a second inverse processing module, integrated into the processing server. The invention also relates to a method of digital telecommunications.

FIELD OF THE INVENTION

The present invention relates to the field of digitaltelecommunications. More specifically, the present invention relates toan access network for terminals of a digital telecommunications system,said access network comprising base stations capable of receivingradiofrequency signals transmitted by said terminals, and possiblycapable of transmitting radiofrequency signals towards the terminals.

BACKGROUND OF THE INVENTION

As known, digital telecommunications systems implement, to exchangebinary data, a predefined physical layer protocol which particularlyaims at converting said binary data into a radiofrequency signal thatcan be transmitted in a predefined frequency band.

A physical layer protocol generally provides a succession of predefinedsteps.

In the case of a transfer of binary data from a terminal to a basestation, the physical layer protocol provides, on the terminal side,steps applied to a binary data flow. These steps are, in particular, amodulation step, during which the binary data are converted into symbols(for example, BPSK, DBPSK, QPSK, 16 QAM, etc.), and a frequency shiftstep, to obtain a radiofrequency signal centered on a predefined centralfrequency.

On the base station side, the physical layer protocol provides applyingto a radiofrequency signal received from the terminal a processinginverse to that applied in transmit mode. Particularly, theradiofrequency signal should be frequency-shifted to obtain a basebandsignal (that is, a signal centered on a substantially zero centralfrequency). The baseband signal, theoretically corresponding to a symbolsequence, is then demodulated to obtain binary data which, in theabsence of errors, are equal to the binary data transmitted by theterminal.

The same steps are applied, in the case of a bidirectionaltelecommunications system, for a transfer of binary data from a basestation to a terminal.

It should be noted that the physical layer protocol may provide manyother steps, for example, an error correction coding step, aninterlacing step, a filtering step, etc.

Further, such a physical layer protocol generally provides insertingcontrol data intended to ease the inverse physical layer processing.

Indeed, the tasks to be performed in receive mode are by a much greaternumber than in transmit mode since it is generally necessary to detectwhether a radiofrequency signal has been transmitted, to estimate thetime of beginning of said radiofrequency signal (time synchronization)and the central frequency of said radiofrequency signal (frequencysynchronization), to estimate the propagation channel in order tocompensate for its effects, etc.

As a result, there is a large number of inverse processing operations tobe performed in receive mode, which requires a high calculation power.This is all the more critical for base stations, which may have tosimultaneously receive binary data from several terminals. Further, basestations perform other operations, relative to the processings ofprotocol layers which use the physical layer services (for example, MAC,TCP/IP, etc.).

SUMMARY OF THE INVENTION

The present invention aims at overcoming all or part of the limitationsof prior art solutions, and particularly those discussed hereabove, byproviding a solution which enables to decrease the calculation powernecessary for the base stations of a digital telecommunications systemaccess network.

Further, the present invention also aims at providing such a solutionwhich enables, in certain cases, to improve the performance of thetelecommunications system access network.

For this purpose, and according to a first aspect, the invention relatesto an access network for terminals of a digital telecommunicationssystem, said access network comprising base stations capable ofreceiving radiofrequency signals transmitted by said terminals, eachterminal comprising a physical layer processing module capable offorming a radiofrequency signal from binary data in accordance with apredefined physical layer protocol. For at least one base station,called “partial station”, an inverse physical layer processing, enablingto extract binary data from a radiofrequency signal formed in accordancewith the physical layer protocol, is distributed between said partialstation and a processing sever (32) distinct from said partial station.An inverse physical layer processing module is made up, for said partialstation, of a first inverse processing module, integrated in saidpartial station and capable of forming intermediate data from aradiofrequency signal received from a terminal, and a second inverseprocessing module, integrated in the processing server, and capable ofextracting binary data from said intermediate data.

According to specific embodiments, the access network may comprise oneor a plurality of the following characteristics, taken alone oraccording to all technically possible combinations.

In a specific embodiment, the access network comprises at least anotherfirst inverse processing module, integrated in the processing server orin another partial station distinct from said processing server, said atleast another inverse processing module also being associated with thesecond inverse processing module of the processing server.

In a specific embodiment, each first inverse processing module isconfigured to include, in the intermediate data, data, estimated by saidfirst inverse processing module, relative to one or a plurality ofcharacteristics of the radiofrequency signal from which saidintermediate data are formed, called “signal identification data”, andthe second inverse processing module of the processing server isconfigured to identify, by comparison of the signal identification dataincluded in intermediate data received from different first inverseprocessing modules, the intermediate data corresponding toradiofrequency signals received from a same terminal.

In a specific embodiment, the second inverse processing module of theprocessing server is configured to combine intermediate data, receivedfrom different first inverse processing modules, corresponding toradiofrequency signals received from a same terminal. As a variation,the second inverse processing module of the processing server isconfigured to perform a selection of intermediate data from amongintermediate data, received from different first inverse processingmodules, corresponding to radiofrequency signals received from a sameterminal.

According to a second aspect, the invention relates to a method ofdigital telecommunications between a terminal and an access network,comprising a step of forming, by the terminal, of a radiofrequencysignal from binary data in accordance with a predefined physical layerprotocol, and a step of extraction, by the access network and byapplying an inverse physical layer processing, of binary data from theradiofrequency signal received from the terminal. According to theinvention, for at least one base station of the access network, called“partial station”, the inverse physical layer processing is distributedbetween said partial station and a processing server distinct from saidpartial station, the binary data extraction step comprising the stepsof:

forming, by a first inverse processing module of the partial station, ofintermediate data from the radiofrequency signal received from theterminal by said partial station,

transferring said intermediate data from said partial station to theprocessing server,

extraction, by a second inverse processing module of the processingserver, of binary data from said intermediate data.

According to specific implementation modes, the telecommunicationsmethod may comprise one or a plurality of the following characteristics,taken alone or according to all technically possible combinations.

In a specific implementation mode, the radiofrequency signal transmittedby the terminal being received by at least two first inverse processingmodules of distinct base stations forming intermediate data, said twofirst inverse processing modules being connected to a same secondinverse processing module, the step of extraction by said second inverseprocessing module comprises identifying the intermediate data formed bydifferent base stations which correspond to radiofrequency signalsreceived from a same terminal.

In a specific implementation mode, the step of extraction by the secondinverse processing module comprises combining the intermediate dataidentified as corresponding to radiofrequency signals received from asame terminal. As a variation, the step of extraction by said secondinverse processing module comprises selecting intermediate data fromamong the intermediate data identified as corresponding toradiofrequency signals received from a same terminal.

In a specific implementation mode, the forming step comprises inserting,into the intermediate data, a parameter representative of asignal-to-noise ratio of the radiofrequency signal, and the combinationor the selection of intermediate data formed by different base stationsis performed according to said parameters included in said intermediatedata.

In a specific implementation mode, the forming step comprises insertingin to the intermediate data, an identification code specific to the basestation having formed said intermediate data.

In a specific implementation mode, the forming step comprises inserting,into the intermediate data, data estimated by the first inverseprocessing module, relative to one or a plurality of characteristics ofthe radiofrequency signal from which said intermediate data, called“signal identification data”, are formed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading of thefollowing description, given as a non-limiting example, in relation withthe drawings, which show:

FIGS. 1 a, 1 b, and 1 c: embodiments of a digital telecommunicationssystem according to the invention,

FIG. 2: a diagram illustrating the main steps of a digitaltelecommunications method according to the invention,

FIG. 3: a diagram illustrating an example of inverse physical layerprocessing,

FIG. 4: a diagram illustrating the main steps of a preferred embodimentof a digital telecommunications method according to the invention.

In these drawings, the same reference numerals from one drawing toanother designate the same or similar elements. For clarity, the shownelements are not to scale, unless otherwise mentioned.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a schematically shows an example of a digital telecommunicationssystem 10 according to the invention.

Digital telecommunications system 10 comprises terminals 20 and anaccess network 30 comprising base stations capable of exchangingradiofrequency signals with terminals 20. Terminals 20 access a networkcore 40 via said access network 30.

“Terminal” designates any object capable of communication with an accessnetwork 30 of a digital telecommunications system 10. A terminal 20 maybe fixed or mobile, and may for example appear in the form of a cellphone, of a laptop computer, of a remote-measurement system sensor, etc.

In the following description, the invention is described in the casewhere binary data should be transmitted by a terminal 20 towards accessnetwork 30. It should however be noted that the invention also appliesin the case where binary data should be transmitted in the oppositedirection, that is, where they should be transmitted by access network30 towards a terminal 20.

Each terminal 20 comprises a physical layer processing module capable offorming a radiofrequency signal from binary data according to apredefined physical layer protocol. Access network 30 carries out, inaccordance with said predefined physical layer protocol, the inverseprocessing, to extract the binary data transmitted by a terminal 20according to radiofrequency signals received from a base station ofaccess network 30.

According to the invention, for at least one base station of accessnetwork 30, called “partial station” 31, the inverse processing isdistributed between said partial station 31 and a processing server 32of access network 30, said processing server being distinct from saidpartial station.

“Distinct” means that partial station 31 and a processing server are twodifferent pieces of hardware equipment.

Further, processing server 32 may be distant from partial station 31,said processing server 32 and the partial station being then located indifferent geographical areas, for example, in different buildings, forexample, separated by a few hundred meters, or even more.

Partial station 31 comprises for this purpose a first inverse processingmodule 310 which carries out a first part of the inverse physical layerprocessing operations. First inverse processing module 310 accordinglyforms intermediate data from a radiofrequency signal received form aterminal 20, said intermediate data being different from the binary datato be extracted.

Processing server 32 comprises a second inverse processing module 320,which carries out a second part of the inverse physical layer processingoperations. Second inverse processing module 320 accordingly extractsthe binary data from the intermediate data received from first inverseprocessing module 310. The binary data extracted by second inverseprocessing module 320 being, in the absence of errors, equal to thebinary data transmitted by terminal 20.

It should thus be understood that the intermediate data correspond todata obtained, during the inverse physical layer processing, between theradiofrequency signal and the binary data. The intermediate data areaccordingly different both from the radiofrequency signal and from thebinary data, since:

the intermediate data are obtained from the radiofrequency signal byapplying a first part of the inverse physical layer processingoperations,

the binary data are obtained from the intermediate data by applying asecond and last part of the inverse physical layer processingoperations.

Partial station 31 and processing server 32 each comprise transfer means33 which transfer the intermediate data from said partial station 31 tosaid processing server 32. Any type of adapted transfer means 33 may beused, and it should be understood that the selection of a type ofspecific transfer means 33 is only a variation of implementation of theinvention. Particularly, said transfer means 33 may comprise wired orwireless or combined wired/wireless communication means.

In the example illustrated in FIG. 1 a, all base stations are partialstations 31 connected to a same processing server 32, so that secondinverse processing module 320 of processing server 32 is used by severalpartial stations 31. In other words, inverse physical layer processingoperations subsequent to those carried out by the first inverseprocessing modules 310 of the different partial stations are allcentralized at the level of second inverse processing module 320 ofprocessing server 32.

FIG. 1 b shows a second example of a telecommunications system 10comprising both partial stations 31 connected to a processing server 32,and at least one base station, called “full station” 34, capable ofcarrying out all inverse physical layer processing operations. Fullstation 34 is directly connected to the core of network 40.

FIG. 1 c shows a variation of FIG. 1 b, where processing server 32 is afull station 34, that is, comprising both a first inverse processingmodule 310 and a second inverse processing module 320, having saidinverse processing module 320 also used by partial stations 31.

It should be noted that nothing excludes having, in digitaltelecommunications system 10 according to the invention, severalprocessing servers 32. Thus, each partial station 31 is for exampleconnected to one of processing servers 32, or to a plurality ofprocessing servers 32 for redundancy purposes (should a processingserver 32 break down).

FIG. 2 shows the main steps of a digital telecommunications method 50according to the invention.

As known, digital telecommunications system 50 comprises a step 51 offorming, by a terminal 20, of a radiofrequency signal from binary datain accordance with the predefined physical layer protocol, and a step 52of extraction, by access network 30, of said binary data from theradiofrequency signal received from said terminal 20.

As previously indicated, binary data extraction step 52 comprises,according to the invention, the steps of:

520 forming, by a partial station 31, of intermediate data from theradiofrequency signal received from terminal 20 by said partial station,

521 transferring said intermediate data from said partial station 31 toprocessing server 32,

522 extraction, by processing server 32, of the binary data from saidintermediate data.

Transfer step 521 comprises a step 521 a of transmission, by partialstation 31, of said intermediate data, and a step 521 b of reception, byprocessing server 32, of said intermediate data.

FIG. 3 schematically shows a non-limiting example of inverse physicallayer processing, adapted to the case where terminals 20 are configuredto transit radiofrequency signals in specific frequency sub-bands of afrequency band, called “multiplexing band”.

In this example, the inverse physical layer processing first comprisesan analog processing step E1. During this step, the radiofrequencysignals received by at least one antenna in the multiplexing band arefrequency-shifted to obtain an analog signal in the vicinity of anintermediate frequency.

The inverse physical layer processing then comprises ananalog-to-digital conversion step E2. During this step, the analogsignal is converted into a digital signal by means of analog-to-digitalconverters.

The inverse physical layer processing then comprises a step E3 oftransposition to the frequency domain, during which the digital signalis transposed from the time domain to the frequency domain, to obtain afrequency spectrum of the digital signal. Said transposition to thefrequency domain is for example performed by means of an FFT (“FastFourier Transform”) module.

The inverse physical layer processing then comprises a detection stepE4, during which frequencies for which energy peaks capable ofcorresponding to the presence of a radiofrequency signal transmitted bya terminal 20 are searched for in the frequency spectrum of the digitalsignal. When a detection criterion is verified, for example, when anenergy peak is greater than a predefined threshold value, said energypeak is assumed to correspond to a radiofrequency signal transmitted bya terminal 20, and the central frequency of this radiofrequency signalis estimated.

The inverse physical layer processing the comprises a frequency-shiftingstep E5 during which the digital signal is taken, according to thecentral frequency estimated at detection step E4, around a substantiallyzero central frequency to obtain a so-called “baseband” signal.

The inverse physical layer processing then comprises a demodulation stepE6, during which the symbol demodulation is carried out. Indeed, thebaseband signal is formed of a sequence of symbols (for example, BPSK,DBPSK, QPSK, 16 QAM, etc.) which represent the binary data transmittedby terminal 20. The conversion of this symbol sequence into binary datais carried out at demodulation step E6. In the absence of errors, thebinary data obtained after demodulation step E6 are equal to the binarydata transmitted by terminal 20.

It should be noted that other operations may be performed during theinverse physical layer processing.

For example, during analog processing step E1, a filtering may beperformed to decrease the power of radiofrequency signals outside of themultiplexing band. Further, an automatic gain control (AGC) may also becarried out to match the dynamics of the analog signal with the inputdynamics of the analog-to-digital converters. Further, duringfrequency-shift step E5, the baseband signal may be filtered andsub-sampled, to decrease the quantity of information to be processedduring demodulation step E6. During demodulation step E6, otheroperations may be performed, such as in particular an estimation of thepropagation channel, an estimation of a frequency drift capable ofaffecting the baseband signal, a channel decoding, etc.

The selection of a specific distribution of the inverse physical layerprocessing operations between first inverse processing module 310 andsecond inverse processing module 320 is only a variation ofimplementation of the invention.

Based on the non-limiting example illustrated in FIG. 3, a first exampleof distribution (separation line P1) comprises assigning radiofrequencyprocessing step E1 and analog-to-digital conversion step E2 to firstinverse processing module 310, and assigning all the subsequent steps ofsecond inverse processing module 320.

A second non-limiting example of distribution (separation line P2)comprises assigning all the inverse processing steps to first inverseprocessing module 310 except for demodulation step E6, which is assignedto second inverse processing module 320. Such a distribution enables todecrease the amount of intermediate data to be transferred, particularlywhen the baseband signal is filtered and sub-sampled.

Generally, first inverse processing module 310 always performs at leastone analog-to-digital conversion step, so that the intermediate data aredigital data.

Due to the fact that they do not carry out all the inverse physicallayer processing operations (and thus that they do not perform the upperprotocol layer processings which use physical layer services), partialstations 31 require less calculation power than full stations 34.

Thus, partial stations 31, having a lower manufacturing cost than fullstations 34, may be deployed by a large number to obtain a good coverageof a predefined geographical area. Partial stations 31 will be connectedto one or a plurality of processing servers 32 which, although theyrequire a greater calculation power, will be by a lower number than thepartial stations.

Further, and as described hereafter, the centralizing of part of theinverse physical layer processing operations will enable, in certaincases, to process, for a same terminal 20, the radiofrequency signalsreceived by distant partial stations 31, and thus to improve the qualityof the propagation channel by introducing a space diversity in receivemode.

In the following description, the case where all inverse physical layerprocessing operations are carried out by first inverse processingmodules 310, except for the symbol demodulation (step E6 in FIG. 3),which is performed by a second inverse processing module 320 ofprocessing server 32, is considered, without this being a limitation.

FIG. 4 shows a preferred embodiment of a digital telecommunicationsmethod 50 according to the invention.

As compared with the example illustrated in FIG. 2, the case where theradiofrequency signal transmitted by terminal 20 is received by twopartial stations 31 a and 31 b, is considered, without this being alimitation.

What is described hereafter in the case of two partial stations 31 a, 31b can also be applied to the case where said radiofrequency signal isreceived by a partial station 31 and a full station 34 integratingprocessing server 32. In other words, what is discussed hereafterapplies as soon as a second centralized inverse processing module 320and at least two first inverse processing modules 310 are available intwo different base stations, one at least of which is a partial station31 distant from said second inverse processing module 320.

Each partial station 31 a, 31 b then executes step 520 of formingintermediate data from the radiofrequency signal that said partialstation 31 a, 31 b has received, as well as transmission step 521 a ofintermediate data transfer step 521. Processing server 32 executes, foreach partial station 31 a, 31 b, reception step 521 b of intermediatedata transfer step 521.

Preferably, and for each partial station 31 a, 31 b, forming step 520comprises inserting, into the intermediate data transferred toprocessing server 32, an identification code specific to said partialstation having formed said intermediate data.

Due to the presence of an identification code in the intermediate data,processing server 32 may directly determine, from received intermediatedata, which intermediate data are received from different partialstations 31 a, 31 b.

The identification code may take any shape enabling processing server 32to separate the intermediate data received from different partialstations 31 a, 31 b. According to a non-limiting example, theidentification code of a partial station 31 corresponds to informationrelative to the position of said partial station 31 a, 31 b, such as theGPS (“Global Positioning System”) coordinates of said partial station.Such an identification code then enables processing server 32 todetermine which partial stations 31 a, 31 b are close and accordinglycapable of receiving radiofrequency signals transmitted by a sameterminal 20.

Preferably and for each partial station 31 a, 31 b, forming step 520comprises inserting, into the intermediate data transferred toprocessing server 32, data relative to one or a plurality ofcharacteristics of the radiofrequency signal from which saidintermediate data are formed, called “signal identification data”.

Due to the presence of signal identification data in the intermediatedata, processing server 32 can directly determine from intermediate datareceived from different partial stations which of said intermediate dataare likely to correspond to radiofrequency signals received from asingle terminal 20.

It should be noted that partial stations 31, when they have formedintermediate data, cannot know offhand the identity of terminal 20having transmitted the received radiofrequency signal. Indeed, it is notprovided, in current physical layer protocols, to assign a physicallayer identifier to each terminal 20. Identifiers are provided at thelevel of upper protocol layers (MAC, IP addresses, etc.) to whichpartial stations 31 do not have access since they do not perform eitherthe upper protocol layer processings which use the physical layerservices.

Certain characteristics of the radiofrequency signal may however allowor ease the identification, at the level of processing server 32, ofintermediate data capable of corresponding to radiofrequency signalstransmitted by a same terminal 20. However, these characteristics of theradiofrequency signal will generally no longer be available in theintermediate data (for example, the central frequency of theradiofrequency signal is no longer available if the intermediate datacorrespond to a baseband signal).

The inserting, into the intermediate data, of identification datacorresponding to estimated characteristics of the radiofrequency signalthus enables processing server 32 to have information easing theidentification of intermediate data corresponding to radio electricsignals transmitted by a same terminal 20. Without the insertion ofidentification data, such information could most often no longer beobtained by said processing server.

Various types of signal identification data may be considered, accordingto the type of multiplexing used at the physical layer level. Forexample, if terminals 20 are configured to transmit in differentfrequency bands, intermediate data forming step 520 may compriseestimating the central frequency of the received radiofrequency signaland inserting this estimation, as signal identification data, in theformed intermediate data. The intermediate data having their centralfrequencies estimated may be considered as likely to correspond toradiofrequency signals transmitted by a same terminal 20.

As a complement or as a variation, intermediate data forming step 520may comprise estimating the radiofrequency signal receive time andinserting this estimate, as signal identification data, into the formedintermediate data. The intermediate data having substantially equalestimated receive times can be considered as likely to correspond toradiofrequency signals transmitted by a same terminal 20.

As a complement or as a variation, if terminals 20 are configured to usedifferent spread codes (CDMA, “Code Division Multiple Access”),intermediate data forming step 520 may comprise estimating the spreadcode used in the received radiofrequency signal and inserting thisestimate, as signal identification data, into the formed intermediatedata. The intermediate data having equal estimated spread codes can beconsidered as likely to correspond to radiofrequency signals transmittedby a same terminal 20.

It should thus be understood that, due to the insertion by partialstations 31 a, 31 b of the partial station identification code and ofthe signal identification data, processing server 32 is capable ofseparating the intermediate data received from different partialstations and, among these intermediate data, of identifying which arecapable of corresponding to radiofrequency signals received from a sameterminal 20.

Accordingly, given that processing server 32 carries out the finaloperations of the physical layer protocol, in particular the symboldemodulation, said processing server will be capable of using the spacediversity in receive mode provided by the different partial stations 31a, 31 b.

It should be noted that the space diversity used by the invention is a“spatial macro-diversity” since partial stations 31 a, 31 b (andaccordingly the receive antennas of said partial stations) are locatedin different geographical areas. In practice, said partial stations 31a, 31 b may be spaced apart by a few hundred meters, or even more, sothat propagation channels between a terminal 20 and each of said partialstations will generally be statistically independent.

The spatial macro-diversity used by telecommunications system 10according to the invention should be distinguished from the spatialmicro-diversity currently used in certain digital telecommunicationssystems. Thus, spatial micro-diversity comprises equipping a same basestation with a plurality of co-located receive antennas. It should beunderstood that due to the fact that said receive antennas areco-located, it is difficult to significantly draw them away from oneanother, so that the propagation channels between a terminal and each ofthe receive antennas of a same base station will generally becorrelated.

It should be noted that nothing excludes, according to the invention,also exploiting spatial micro-diversity by equipping one or severalpartial stations 31 a, 31 b with several receive antennas.

To exploit spatial macro-diversity, processing server 32 preferablycombines the intermediate data received from different partial stations31 a, 31 b identified as corresponding to radiofrequency signalsreceived from a same terminal 20. This combination may be performedaccording to any known combination method known in the exploitation ofspatial micro-diversity in receive mode. For example, such a combinationmay be performed to maximize the signal-to-noise ratio, such acombination being known as “Maximum Ratio Combining” (MRC).

As a variation, processing server 32 selects intermediate data fromamong the intermediate data received from different partial stations 31a, 31 b identified as corresponding to radiofrequency signals receivedfrom a same terminal 20. This selection may be performed according toany selection method known in the exploitation of spatialmicro-diversity in receive mode. For example, it is possible to selectthe intermediate data which have the best signal-to-noise ratio.

To ease the exploiting of spatial macro-diversity in receive mode,forming step 520 preferably comprises inserting, into the intermediatedata transferred to processing server 32, at least one parameterrepresentative of a signal-to-noise ratio of the radiofrequency signal.Processing server 32 then combines or selects the received intermediatedata according to said parameters included in said intermediate data.

For example, the parameter inserted into the intermediate datacorresponds to an estimate of the signal-to-noise ratio, to an estimateof the propagation channel, to an estimate of the receive power, to thegain applied due to the automatic gain control (AGC), etc.

Thus, the intermediate data of partial stations 31 a, 31 b are shapedaccording to a predefined intra-physical layer communication protocol.

For example, the intermediate data formed from a radiofrequency signalmay be organized in several messages transmitted over a transfer channelbetween a partial station 31 a, 31 b and processing server 32. Forexample, in the case where processing server 32 only carries out thesymbol demodulation (step E6 in FIG. 3), the transmitted messages maytake the following form.

A first transfer channel initialization message may be transmitted bypartial station 31 a, 31 b, with a format of [Id Fi SNR] type, where:

Id is the partial station identification code,

Fi is the initial central frequency of the radiofrequency signal, and

SNR is the signal-to-noise ratio of the radiofrequency signal.

Then, and for each symbol of the baseband signal, partial station 31 a,31 b transmits a message with a format of [Id Tn Fi Fcn n Xn Yn] type,where:

n is the index of the symbol transmitted in this message,

Tn is the receive time of the symbol of index n,

Fcn is the central frequency of the radiofrequency signal at time Tn,

Xn and Yn are the coordinates of the symbol of index n in the complexplane (constellation).

The inserting of current central frequency Fcn is particularlyadvantageous in the case where the frequency drift of the radiofrequencysignals transmitted by a terminal 20 is high. This will particularlyoccur in telecommunications systems having a narrow band, for example,approximately, from a few Hertz to a few hundred Hertz, where terminals20 are equipped with inexpensive frequency synthesis means, for whichthe frequency drift may be greater than the bandwidth of said system.

Inserting initial central frequency Fi in each message enablesprocessing server 32 to identify consecutive messages as correspondingto a same radiofrequency signal. Indeed, initial central frequency Fidoes not vary, while central frequency Fcn may vary from one message toanother if the frequency drift is significant.

More generally, it should be noted that the embodiments andimplementation modes considered hereabove have been described asnon-limiting examples, and that other variations may accordingly beenvisaged.

In particular, it should be noted that it is possible, according toother examples, to distinguish the intermediate data received fromdifferent partial stations 31 a, 31 b otherwise than by the insertion ofan identification code. For example, the intermediate data may betransferred to processing server 32 by means of different communicationprotocols for which specific addresses are previously assigned topartial stations 31 a, 31 b and to processing server 32. According to anon-limiting example, the intermediate data are encapsulated in IP(“Internet Protocol”) datagrams, and processing server 32 distinguishesthe intermediate data received from different partial stations 31 a, 31b according to the IP addresses of said partial stations. However, sucha distinction, based on the IP address of partial stations 31 a, 31 b,requires a specific interface enabling second inverse processing module320 to recover the source IP address of the IP datagram whereintermediate data were encapsulated. It should be understood that such aspecific interface is not necessary if a partial station identificationcode is inserted into the intermediate data.

Further, it is possible, according to other examples, to identify theintermediate data likely to correspond to radiofrequency signalstransmitted by a same terminal 20 otherwise than by inserting signalidentification data. For example, in the case where partial stations 31a, 31 b only carry out the operations until the analog-to-digitalconversion, most of the inverse physical layer processing being carriedout by processing server 32, it should be understood that it is saidprocessing server which can determine signal identification data(central frequency, receive time, etc) to determine whether aradiofrequency signal transmitted by a terminal 20 has been received bya plurality of partial stations 31. According to another example,processing server 32 may use an identifier of terminal 20 inserted intothe upper protocol layers (MAC, IP addresses, etc.). However, thisimposes for processing server 32 to extract the binary data from thereceived intermediate data, and to carry out the upper physical layerprocessing operations before being able to identify which intermediatedata are likely to correspond to radiofrequency signals transmitted by asame terminal 20. In a context of combination or selection of theintermediate data, this results in a significant increase of theprocessing operations carried out by processing server 32.

Further, it is possible, according to other examples, to exploit themacro-diversity without inserting parameters representative of thesignal-to-noise ratio. For example, it is possible to pre-compensate,according to the signal-to-noise ratio, the symbols transmitted toprocessing server 32, so that processing sever 32 will only have todirectly combine the symbols or to select the symbols having thegreatest amplitude.

The foregoing description clearly illustrates that, by its differentfeatures and their advantages, the present invention achieves its aims.

In particular, the distribution of the inverse physical layer processingoperations between a partial station and a processing server providesless complex partial stations.

Further, the centralizing of certain inverse physical layer processingoperations (in particular, symbol demodulation) at the level of saidprocessing server enables to improve the performance of the digitaltelecommunications system by exploiting a spatial macro-diversityprovided by distant partial stations located in different geographicalareas.

1. An access network for terminals of a digital telecommunicationssystem, said access network comprising base stations capable ofreceiving radiofrequency signals transmitted by said terminals, eachterminal comprising a physical layer processing module capable offorming a radiofrequency signal from binary data in accordance with apredefined physical layer protocol, characterized in that, for at leastone base station, called “partial station”, an inverse physical layerprocessing, enabling to extract binary data from a radiofrequencysignal, is distributed between said partial station and a processingserver distinct from said partial station, an inverse physical layerprocessing module being made up of a first inverse processing module,integrated in said partial station and capable of forming intermediatedata from a radiofrequency signal received from a terminal, and a secondinverse processing module, integrated in the processing server, andcapable of extracting binary data from said intermediate data.
 2. Theaccess network of claim 1, characterized in that said access networkcomprises at least another first inverse processing module, integratedin the processing server or in another partial station distinct fromsaid processing server, said at least another inverse processing modulealso being associated with the second inverse processing module of theprocessing server.
 3. The access network of claim 2, characterized inthat: each first inverse processing module is configured to include, inthe intermediate data, data, estimated by said first inverse processingmodule, relative to one or a plurality of characteristics of theradiofrequency signal from which said intermediate data are formed,called “signal identification data”, the second inverse processingmodule of the processing server is configured to identify, by comparisonof the signal identification data included in intermediate data receivedfrom different first inverse processing modules, the intermediate datacorresponding to radiofrequency signals received from a same terminal.4. The access network of claim 3, characterized in that the signalidentification data comprise an estimate of a central frequency of theradiofrequency signal and/or an estimate of a time of reception of saidradiofrequency signal.
 5. The access network of claim 2, characterizedin that the second inverse processing module of the processing server isconfigured to combine intermediate data, received from different firstinverse processing modules, corresponding to radiofrequency signalsreceived from a same terminal.
 6. The access network of claim 2,characterized in that the second inverse processing module of theprocessing server is configured to select intermediate data from amongintermediate data, received from different first inverse processingmodules, corresponding to radiofrequency signals received from a sameterminal.
 7. A method of digital telecommunications between a terminaland an access network, comprising a step of forming, by the terminal, ofa radiofrequency signal from binary data in accordance with a predefinedphysical layer protocol, and a step of extraction, by the access networkand by applying an inverse physical layer processing, of binary datafrom the radiofrequency signal received from the terminal, characterizedin that, for at least one base station of the access network, called“partial station”, the inverse physical layer processing is distributedbetween said partial station and a processing server of said accessnetwork distinct from said partial station, the binary data extractionstep comprising the steps of: forming, by a first inverse processingmodule of the partial station, of intermediate data from theradiofrequency signal received from the terminal by said partialstation, transferring said intermediate data from said partial stationto the processing server, extraction, by a second inverse processingmodule of the processing server, of binary data from said intermediatedata.
 8. The method of claim 7, characterized in that the radiofrequencysignal transmitted by the terminal is received by at least two firstinverse processing modules of distinct base stations formingintermediate data, said two first inverse processing modules beingconnected to a same second inverse processing module, the step ofextraction by said second inverse processing module comprisesidentifying the intermediate data formed by different base stationswhich correspond to radiofrequency signals received from a sameterminal.
 9. The method of claim 8, characterized in that the step ofextraction by the second inverse processing module comprises combiningthe intermediate data identified as corresponding to radiofrequencysignals received from a same terminal.
 10. The method of claim 8,characterized in that the step of extraction by said second inverseprocessing module comprises selecting intermediate data from among theintermediate data identified as corresponding to radiofrequency signalsreceived from a same terminal.
 11. The method of claim 9, characterizedin that the forming step comprises inserting, into the intermediatedata, a parameter representative of a signal-to-noise ratio of theradiofrequency signal, and in that the combination or the selection ofintermediate data formed by different base stations is performedaccording to said parameters included in said intermediate data.
 12. Themethod of claim 7, characterized in that the forming step comprisesinserting, into the intermediate data, an identification code specificto the base station having formed said intermediate data.
 13. The methodof claim 7, characterized in that the forming step comprises inserting,into the intermediate data, data, estimated by the first inverseprocessing module, relative to one or a plurality of characteristics ofthe radiofrequency signal from which said intermediate data called“signal identification data” are formed.
 14. The method of claim 13,characterized in that the signal identification data comprise anestimate of a central frequency of the radiofrequency signal and/or anestimate of a time of reception of said radiofrequency signal.